The present invention relates to a device for front lighting of a flat display.
A device for backlighting a flat display is described in German Patent No. 195 38 893. In this device, the light of a light source is injected into a fiber optic plate, diffusion particles being added to the material of the fiber optic plate for diffusion of light. However, in the case of a device for backlighting a display, the backlighting must be operated continuously during observation by a user for the display to be properly readable. To permit operation without backlighting only with daylight, a layer of a reflective material must be arranged behind the display. If the reflective material is arranged in front of the backlighting, it must allow the light from the backlighting to pass through. Therefore, it must be at least partially transparent. This reduces the efficiency in reflection of daylight lighting up the display. Furthermore, it is also known that in order to combine good readability in operation with ambient light on one hand and good readability in backlighting operation of the flat display on the other hand, a fiber optic plate having microprisms must be arranged in front of the flat display. However, to produce a fiber optic plate having microprisms, a mold that is very expensive to manufacture is necessary for production by an injection molding method, for example. In addition, the microprisms must not interfere with readability.
A device according to the present invention has the advantage that incident light striking the fiber optic plate is deflected to the display by the light scattering particles, thereby lighting up the display. Front lighting of the display is thus possible in a simple and inexpensive manner. This has only a negligible effect on readability in operation with ambient light.
It may be advantageous if the fiber optic plate is at least a part of a front plate of a housing for the flat display. The flat display is thus covered by the fiber optic plate and is therefore protected from contact, soiling and/or destruction. In comparison with a display design having backlighting, this makes it possible to reduce the size of the housing for the flat display, because instead of a flat display for the backlighting and a cover, a fiber optic plate is all that is needed.
Furthermore, it may be advantageous if light of a light source is injected into the fiber optic plate over at least one reflecting surface. Therefore, it is possible for the light source not to be arranged directly next to the fiber optic plate, but instead a position of the light source which is favorable for the design of the entire display device can be selected, and the light emitted by it is injected into the fiber optic plate via the reflective surface.
Furthermore, it may be advantageous to provide a fiber optic wedge in a side face of the fiber optic plate, making it possible to use only a single light source, almost a punctiform light source, for the backlighting.
In addition, it may be advantageous to arrange a light-sensitive electric component on the device, and to measure the ambient brightness by way of the light-sensitive component. The brightness of the lighting of the flat display is regulated as a function of an analysis of the electric current flowing through the light-sensitive component or the voltage drop across the light-sensitive component. This makes it possible for the lighting to be turned off when there is sufficient ambient brightness, thereby reducing the total power consumption of the flat display in comparison with lighting operated continuously. Due to the automatic shutdown, the front lighting cannot inadvertently remain in operation when there is increasing ambient brightness. However, if the ambient brightness decreases, the front lighting is automatically switched on.
In addition, it may be advantageous to arrange a reflector on the side of the display facing away from the fiber optic plate, so that the reflector can deflect light passing through the flat display and reflect it back to an observer. This improves the overall brightness of the display.
In addition, it may be advantageous for the diffusion particles to constitute a maximum of 2% by volume of the total volume of the fiber optic plate. Due to this small amount of diffusion particles, readability of the display is influenced minimally at most.